When we hear the term “green roofing” many things come to mind. This term can refer to truly green roofs such as garden roofs, vegetative roofs or what National Roofing Contractors Association has come to call landscape roofs.
These are typically low-slope roofing systems with vegetation in a growing medium designed to cool a building through moisture evaporation from the plants and to control stormwater runoff.
But “green” roofing can also describe a roof system that has components of sustainability. Did you realize metal roofing can be that type of roof? Yes, a metal roof can be an environmentally responsible choice for a building owner. A roof that minimizes its impact on the environment, from cradle to grave or one that lowers cooling energy usage and the corresponding greenhouse gas emissions associated with that energy, can be a green roof.
Besides, the U.S. Green Building Council defines green buildings using three components of a design: the impact on the planet, the impact on the people occupying the building and the financial impact on the building owner. The impact on the planet is the true green aspect of sustainability. This refers to the carbon footprint or the environmental impact of the building’s materials, construction practice and operation over time. Let’s take a look at how metal roofing can contribute to a building’s impact on the planet.
Cool metal roofing can contribute to the green building design as defined by USGBC. Generally speaking a cool metal roof is one whose surface has relatively high solar reflectance and high thermal emittance values. It helps to lower the surface temperature, thereby lowering the heat gain into the building and reducing the cooling energy requirements.
Another form of cool metal roofing is a roof installed in such a way as to create a continuous airspace from eave to ridge. That type of installation technique is called “above sheathing ventilation.” The air space created between the roof material and the sheathing allows for natural convective cooling to take place, which dissipates heat build up below the metal roof surface. Oak Ridge National Laboratory has determined that ASV can lower the heat flow into the attic space below the roof by 30 percent when compared to common direct-to-deck installations. When ASV is combined with a cool or solar reflective metal roof surface, the heat gain can be reduced by up to 45 percent. Metal roofing can be installed with special clips, spacers or battens/counter-battens to create the continuous air space. Some metal roofing products have an inherent air space created by the nature of the profile.
Buildings consume 39 percent of our nation’s energy, which is higher than the consumption of the transportation sector and the industrial sector. Today’s designers are looking at any way to reduce the use of energy in a building. A cool metal roof can certainly help to reduce cooling energy. This is a cost savings to the building owner and a way to reduce CO2 emissions from the fossil fuel fired power plant. It can also help to mitigate urban heat island effects in large metropolitan areas where local air temperatures can be 6-12 degrees higher than in the surrounding suburbs.
Metal roofing in general has a high-recycled content that lowers its impact on the environment during manufacturing. Metal is also fully recyclable at the end of its service life, which eliminates the old material from entering the solid waste stream. To that point, according to the Steel Framing Alliance, more steel is recycled than aluminum, paper, glass and plastic combined.
The longevity of metal roofing has environmental impacts as well. By delaying the tear-off of a metal roof for decades, the impact from manufacturing more replacement material is significantly reduced. Most coatings used on metal roofing and natural metals in particular, retain their appearance and properties for decades. Hence, the initial energy efficiency, color and reflectivity allow building owners to enjoy the benefits of the product for a very long service life. The durability of metal roofing also plays a role in a building’s re-use. Often the metal roof is performing very well at a time when a building may be renovated for other reasons. Again, avoiding the replacement of the roof has a great environmental or green impact.
Finally, a metal roof can be part of a building design that harvests rainwater. Increasing the conservation and efficient use of water is becoming more important to owners and communities.
Water shortages in regions of the country and around the world are creating dire conditions for the population. By incorporating a metal roof with a water collection system for gray water usage or irrigation will reduce the amount of potable water for those uses. The fact potable water has high-embedded energy for the extraction, treating and transportation of the water to a building means any effort to reduce its use will have positive environmental and energy impacts.
In today’s green building world, there are many rating, labeling and certification programs. The EPA’s Energy Star program includes roofing products. Many metal roofing products meet the Energy Star criteria for initial and aged solar reflectance values.
In addition the USGBC’s Leadership in Energy and Environmental Design building certification program allows cool metal roofing to indirectly contribute to the points awarded to a building based on the integrated design of all components. One point can be obtained for a Sustainable Site credit toward reducing urban heat island effects, based on the Solar Reflectance Index criteria. Many metal roofing products can meet that criterion, thereby allowing a metal roof to be part of the building design.
Metal roofing has many other attractive features that benefit a building owner. Its high strength to weight ratio, non-combustibility, resistance to wind, hail and seismic activity and its design flexibility with unlimited choices in colors, textures and profiles make metal a popular choice for a roofing material. Combining those important features with the green aspect of metal roofing, only highlights why metal’s share of the roofing market continues to grow.
Scott Kriner is the president and founder of Green Metal Consulting, Inc. He is a LEED Accredited Professional with more than 25 years of metal construction industry experience. His company is a member of the U.S. Green Building Council, the California Association of Building Energy Consultants and the Residential Energy Services Network. He can be reached by email at email@example.com or by phone at (610) 966-2430. You can also visit him on the web at www.greenmetalconsulting.com.